Polkadot: Support errors according to `solc`

[xermicus]

Implement Panic and custom errors for the Polkadot target:

• Allow catching Panic in sema
• Allow custom errors in sema
• Implement selector calculation for custom errors
• Refactor try-catch in codegen to allow catch clauses on Panic errors in
• Add any custom errors in the metadata

[xermicus]

Closes #698